Commercial trucks are commonly manufactured and sold with only a vehicle cab mounted on the necessary running gear, but with no other body structure mounted on the vehicle frame rails so that such trucks may be custom outfitted with whatever bodies and work apparatus as may be needed or desirable to suit a particular utility or work purpose. For example, such trucks may be equipped with specially designed and configured cargo beds, storage cabinetry, associated power equipment such as air and hydraulic compressors, pumps, lift cranes, outrigger structures for stabilizing the truck body when situated at a job site, etc.
Third party manufacturers who purchase basic trucks from major vehicle manufacturers must design and retrofit to the truck frame appropriate sub-frame structures to support such specialty equipment. Competing considerations often must be accommodated in the design of the necessary support structures. For example, in trucks to be equipped with cranes or like lifting mechanisms, the sub-frame structures must be of sufficient strength and rigidity to withstand the forces and loads imposed during lifting operations. While sub-frame structures can be constructed of larger, heavier, thicker materials, or otherwise reinforced to carry such loads and forces, each basic truck comes from the manufacturer with a rating of the maximum load capacity that can be accommodated by the vehicle suspension. Reinforcement of sub-frame support structures typically adds significant extra weight on the vehicle suspension which in turn limits the utility of the vehicle without exceeding the manufacturer's load capacity rating. Thus, there is generally a practical limit to how much a truck sub-frame structure can be reinforced without detracting from the intended utility of the vehicle. On the other hand, insufficient reinforcement of a sub-frame structure poses the risk of damage to the sub-frame structure or even failure of the truck under load, or in extreme cases potential injury to workmen.
There therefore exists a significant but yet unmet need in the utility truck industry for a design for a vehicle sub-frame structure that provides significant reinforced strength to the structure but with minimal added weight.